It is known to provide a container with an opening for adding or removing material to the container, and the opening may have a closure for sealing the opening. A common form of closure is a tapered plug, usually made of cork, and the opening typically has a cylindrical or tapered interior surface which cooperates with the exterior surface of the plug to seal the opening. The upper surface of the opening is planar, and the plug is inserted into the opening in a direction perpendicular to this planar surface and removed in an opposite direction. Another common type of opening is a cylindrical neck having threads for receiving matching threads on a cap. The cap is applied to the neck by rotating it to engage the matching threads.
These forms of closures have many disadvantages. For example, the simple, tapered plug may be accidentally removed from the opening by an increase of pressure within the container. This is because the plug is held in the neck only by friction between the neck and the plug. The provision of a wire mesh or similar device to secure the plug is expensive and cumbersome. The screw-on cap is difficult to use since it requires a twisting motion. Furthermore, this type of cap seals by the cooperation between an upper edge of the neck and a small, annular portion of the cap, and this is frequently inadequate.
Various attempts have been made to improve upon these closures. U.S. Pat. No. 3,405,832 (Lukesch, et al.) shows a stopper which includes a tapered, annular portion for engaging a similarly-shaped portion of the neck of a container. Below the tapered portion of the stopper, is a ridge for engaging a lip on the container below the neck. The stopper is deformable so that the ridge on the stopper must be compressed to pass the lip of the container, thereby securing the stopper to the container. U.S. Pat. No. 3,095,995 (Foster) shows a plug pivotally attached to a container for sealing an opening in the container. The upper surface of the container having the opening is generally flat, and the plug is resilient for sealingly engaging surfaces of the opening. U.S. Pat. No. 3,362,565 (McCormick) shows a container having an opening formed by a shoulder which is engaged by a sealing bead on the lid.